Permanent deformation testing in the laboratory and rutting measurements on the highway continue to present complicated situations to the engineer attempting to understand mixture performance. The development of new testing procedures promises to provide a better understanding of material behavior. Although this increasingly complex technology continues to provide more information, a vast amount of information available today is not being analyzed in a fundamentally sound manner. Accurate rutting comparisons are needed to help the highway engineer today while the new technology undergoes development, testing, and validation. These procedures must provide data that are applicable to field studies and consistent for use in the new Strategic Highway Research Program testing procedures. Field measurements of permanent deformation indicating that previous modeling attempts using field measurements may have been fundamentally flawed are discussed. Predictions of rut depth development in the field are not always adequately presented to truly represent the interaction of mix parameters with performance. Previous models have not considered the developmental phases of rutting. The result is that different materials are not compared consistently. These misapplications produce comparisons of mixtures that cannot accurately indicate the true performance potential of the various mixtures. Correct procedures that provide representative comparisons of mix quality are presented.